Name:	cyn_FinancingReceivableModificationsIncreaseDecreaseInRecordedInvestment
Namespace Prefix:	cyn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Represents specific reserves related to troubled debt restructured loans.

No definition available.

Name:	cyn_FinancingReceivableModificationsSpecificReserves
Namespace Prefix:	cyn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Represents restructured loans that have been returned to accrual status but continue to be reported as impaired.

No definition available.

Name:	cyn_ImpairedRestructuredLoansOnAccrualStatus
Namespace Prefix:	cyn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Name:	us-gaap_FinancingReceivableImpairedLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Number of financing receivables that have been modified by troubled debt restructurings.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 33

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953676-111524

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

Name:	us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18845-111554

Name:	us-gaap_FinancingReceivableModificationsRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Reflects the amount of the write-down related to a troubled debt restructuring.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=cyn_EquityLinesOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Namespace Prefix:
Data Type:	na
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Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_AdjustableRateResidentialMortgageMember
Namespace Prefix:
Data Type:	na
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Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_CommercialLoanMember
Namespace Prefix:
Data Type:	na
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Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_CommercialRealEstateMember
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